Among the clinically used cephalosporin antibiotics, only a few exhibit significant absorption from the gut and are therapeutically useful when administered orally. Cephalexin and cefaclor are two orally effective cephalosporin antibiotics that are highly absorbed. The majority of the cephalosporin antibiotics, however, are effective when administered parenterally. Considerable research work by chemists and microbiologists is directed toward the discovery and development of new orally effective semi-synthetic cephalosporin antibiotics with improved properties, for example, enhanced activity against staphylococci and streptococci, effectiveness against resistant microorganisms, and high absorptivity from the gut.